Live human assessment of depth-dependent corneal displacements with swept-source optical coherence elastography

Abstract

PurposeTo assess depth-dependent corneal displacements in live normal subjects using optical coherence elastography (OCE).MethodsA corneal elastography method based on swept-source optical coherence tomography (OCT) was implemented in a clinical prototype. Low amplitude corneal deformation was produced during OCT imaging with a linear actuator-driven lens coupled to force transducers. A cross-correlation algorithm was applied to track frame-by-frame speckle displacement across horizontal meridian scans. Intra-measurement force and displacement data series were plotted against each other to produce local axial stiffness approximations, k, defined by the slope of a linear fit to the force/displacement data (ignoring non-axial contributions from corneal bending). Elastographic maps displaying local k values across the cornea were generated, and the ratio of mean axial stiffness approximations for adjacent anterior and posterior stromal regions, ka/kp, was calculated. Intraclass correlation coefficients (ICC) were used to estimate repeatability.ResultsSeventeen eyes (ten subjects) were included in this prospective first-in-humans translational study. The ICC was 0.84. Graphs of force vs. displacement demonstrated that, for simultaneously acquired measurements involving the same applied force, anterior stromal displacements were lower (suggesting stiffer behavior) than posterior stromal displacements. Mean ka was 0.016±0.004 g/mm and mean kp was 0.014±0.004 g/mm, giving a mean ka/kp ratio of 1.123±0.062.ConclusionOCE is a clinically feasible, non-invasive corneal biomechanical characterization method capable of resolving depth-dependent differences in corneal deformation behavior. The anterior stroma demonstrated responses consistent with stiffer properties in compression than the posterior stroma, but to a degree that varied across normal eyes. The clinical capability to measure these differences has implications for assessing the biomechanical impact of corneal refractive surgeries and for ectasia risk screening applications.

Heartbeat OCE: corneal biomechanical response to simulated heartbeat pulsation measured by optical coherence elastography

“…OCE with an external excitation source has been used to assess the mechanical properties of the cornea in vivo using dynamic wave propagation methods as well as quasistatic techniques. 19,21,42 However, these techniques have a variety of limitations in acquisition and analysis, such as patient discomfort, nonlinear mechanical behavior, or lengthy imaging times. Since the technique presented in this work does not require complex wave analysis or additional tools to determine tissue mechanical properties, we can assess the mechanical properties of the cornea using only a phase-sensitive OCT system, a ubiquitous tool in ophthalmology and optometry clinics.…”

“…8,[15][16][17][18] Typically, these techniques measure the corneal response to different external forces. [19][20][21][22][23] However, there is growing interest in assessing the tissue mechanical response to intrinsic physiological forces. 24 For example, hemodynamics within the eyeball can cause ocular tissue to experience pulsatile motion known as the ocular pulse.…”

Optical Coherence Elastography-Based Corneal Strain Imaging During Low-Amplitude Intraocular Pressure Modulation

“…While dynamic measurements allow fast imaging speeds and hence reduce motion artifacts, longer time scales, which are relevant for corneal reshaping and disease progression, are not accessible. The only quasi-static assessment of in vivo corneal biomechanics combines OCE with central applanation of the cornea by a gonioscopy lens (De Stefano et al, 2018) requiring contact. Here, spatially resolved cross-sectional maps of axial corneal displacements were obtained by tracking speckle deformation during the applanation (De Stefano et al, 2018).…”

Ultrahigh-sensitive optical coherence elastography

“…A lambda (λ) trigger using a fiber Bragg grating (FBG) as well as a kclock generated by a Mach-Zehnder interferometer (MZI) have been introduced to improve the phase stability, making SS-OCT a more attractive setup in OCE applications 28 . In recent years, several OCE systems based on conventional SS-OCT (SS-OCE COV ) have been proposed 14,[29][30][31][32][33][34][35] , and their feasibilities have been validated through ex vivo and in vivo experiments, demonstrating great potential towards clinical translation. Although these studies have reported subnanometre displacement sensitivities, this is achieved only in system charaterization where a simple common-path configuration is used.…”